Since the 1990s, the State Environmental Protection Administration has put restrictions on the NOx emission from coal-fired power plant boiler (GB 13223-1991) and continuously tightened the emission limit in successive Emission Standard of Air Pollutants for Thermal Power Plants (GB 13223-1996 and GB 13223-2003). According to the latest Emission Standard of Air Pollutants for Thermal Power Plants (GB 13223-2011) released in July 2011, NOx emission from newly-built, expanded and rebuilt coal-fired power plant must meet the limit of 100 mg/m3 (key regions) and 200 mg/m3 (other regions) from Jan. 1, 2012, and all coal-fired power plants completed as of Jan. 1, 2014 must meet the aforesaid standards. In a mature SCR flue gas denitrification technology with high efficiency, catalyst is an important part in the SCR system and its performances will directly affect the denitration effect of the catalyst. Being easily blocked and poisoned, it is inevitable that a catalyst will lose activity during use and inactive catalyst usually will be regenerated for reuse to reduce the cost and the waste stacking space. Therefore, solving the problem of catalyst regeneration will improve the actual emission reduction effect and greatly improve the economy of SCR technology.
Based on the active site theory in catalytic reaction kinetics, catalytic reaction occurs at the active site on catalyst surface and larger specific surface area can offer more surface active sites. Besides, the richer the micropore structure is, the larger the specific surface area is. In terms of pore channel structure, within the scope adaptive to SCR reaction, larger pore volume means larger reaction gas volume contained in the pore structure, which is also beneficial to the catalytic reaction.
In microwave heating technology, high-frequency reciprocating motions of dipole molecules inside the heated object generate “internal friction heat” and cause internal and external heating and temperature rise at the same time without any heat conduction process. With a quick and even heating speed, it requires only a small percentage of energy consumption required by the traditional heating method, and hence has a good development prospect in terms of catalyst regeneration.
After searching existing technical literatures, a Chinese patent CN1686607A discloses a filter unit for regenerating active carbon with microwaves and ultrasonic waves. Fluid flows into a filter via an inlet on a casing cover, runs through active carbon filled in the casing body for filtration and flows out of the filter along a pipe in the active carbon via an outlet on the casing cover. If the active carbon is inactive and needs to be regenerated, the fluid flows into the outlet and flows out of the inlet and microwave irradiation and ultrasonic waves will regenerate the active carbon when turning on the microwave generator and ultrasonic generator, and the fluid will bring out impurities from the regeneration process. Since the regeneration process of denitration catalyst cannot directly occur on site and requires the cleaning and impregnating with various solutions in different containers, SCR process and regeneration process cannot occur in the same container, and method of such patent is unsuitable for regenerating SCR denitration catalyst.
Chinese patent CN1686607A discloses a method for regenerating denitration catalyst by selective catalytic reduction and device therefor. In such regeneration method, poisoned SCR denitration catalyst after actual industrial application successively undergo ultrasonic pretreatment, cleaning with deionized water, impregnating with pore-expanding solution, high-temperature high-pressure evaporation, activating with active material and calcining process, so as to be regenerated for reuse. Such method has certain dangers due to high pressure of the autoclave used; causes waste of the pore-expanding solution like absolute ethyl alcohol; requires ultrasonic cleaning with deionized water for 10 minutes, still standing for 2-3 hours and maintenance under high temperature in the autoclave for a period of time; and requires complete drying of activating liquid after pore-expanding and drying under 105-130° C. for 4-8 hours. Such method takes a long time and great energy consumption due to restriction of the instrument and temperature.